This is still fully possible on Immutable distros (which is why the name is misleading, but unfortunately is what stuck- “image-based” is a better description) and uBlue has a mechanism for it- since they’re delivered using OCI containers, it’s trivial to fork or derive from the project and add, remove or tweak whatever you need. There’s also BlueBuild which is YAML but that’s a third party project.
No, just the FSR2 demo application, which suffered from poor performance regardless of whether or not FSR2 is on.